1. Field of the Invention
The present invention relates to a magnetic sensor and, particularly, to a magnetic sensor including an multi layer thin film which is a lamination of ultra thin films.
2. Description of Related Art
An example of a conventional thin film magnetic sensor of this kind is disclosed in Japanese Patent Publication No. S54-41335 specification. Among other conventional thin film magnetic sensors, a magnetic sensor which uses a single layer of a ferromagnetic thin film to utilize the magnetoresistance effect inherent thereto and obtains an output by specifically patterning the ferromagnetic film has been known.
The above-mentioned thin film magnetic sensor merely utilizes the anisotropic magnetoresistance effect of ferromagnetic thin film. Therefore, an output characteristics thereof depends upon rate of change of magnetoresistance, .DELTA.R/R, which is calculated from crystal parameters of material. Further, the rate of change of magnetoresistance is at most 6.5% at room temperature as disclosed in, for example, T. R. McGuire and R. I. Potter, "Anisotropic Magnetoresistance in Ferromagnetic 3d Alloys", IEEE Trans. Mag, Mag-11, No. 4, P1018 (1975).
In order to obtain a large magnetoresistance change rate .DELTA.R/R in the conventional thin film magnetic sensor, it is necessary to employ either one of methods of lowering temperature, making a pattern width of the film considerably large and making a film thickness very large. However, variable range of the pattern width or the film thickness is about 1 to 2% at most when temperature is fixed at room temperature.
The sensitivity of the magnetic sensor in detecting magnetization intensity of a medium to be detected depends upon the magnetoresistance change rate .DELTA.R/R. Therefore, it is impossible to detect a moving state thereof precisely when the value of the magnetoresistance change rate is small.